For some years, there have appeared on the market a large number of products that monitor vital signs to track disease states. More recently, there has been a shift in emphasis to monitor the vital signs of individuals for whom there is no suspected illness, but for early indications of health problems. Examples of such vital signs are heart rate and motion, blood pressure, and respiration rate. Part of the need is to provide measurements for a period of hours that may span a variety of activities, such as relaxation, physical exercise, and stressful mental activities. Such measurements can be recorded automatically for later analysis, and in some cases, even be accompanied by alarms when there are readings that do not fall within selected limits.
In order for such products to appeal to vast numbers of individuals who are seemingly “well”, they need to be as convenient and unobtrusive as possible, and intrinsically safe. Low cost, small size, light-weight, concealed or ordinary in appearance, ultra-low power consumption, non-invasive, and effortless use are features that will result in the general population enjoying the benefits of extended periods of vital signs monitoring.
Stand-alone wristwatch heart rate instruments, readily available for some years, are not convenient for continuous monitoring; as they require the user to hold the instrument with the opposite hand. Other wearable heart rate instruments are hands free, but they require a harness that goes around the upper torso, and power consumption is considerable.
Existing wearable monitoring products perform a single function, forcing the user to purchase, manage and maintain a separate product for each type of measurement. Hands free heart and respiration rate equipment using eddy currents have been developed, but they are too bulky and require too much power to be successful in the market place discussed above.
The embodiments described in the instant disclosure meet all commercial requirements for size, cost, weight, speed, convenience, power-drain and measurement accuracy. Moreover, for medical applications, eddy current density and power dissipation within the body are far below recognized safety limits. It is shown in the instant document that a fully functioning eddy current instrument here invented will induce within the human body about 5% of the current density amount stated as the safety limit by ICNIRP.